Semiconductor processing furnace outflow cooling system

ABSTRACT

A vertically oriented thermal processor for processing batches of semiconductor wafers held within a processing chamber. The processing chamber is contained within a processing vessel. Processing gases are discharged through a processing chamber outflow. An outflow cooler is included to cool gases exhausting from the processing chamber outflow. The outflow cooler includes a fluid heat exchanger and a flow diverter which directs the exhausting gases against cooled walls of the outflow cooler. The cooler also preferably has a liner which lines a casing to which the heat exchanger is connected.

TECHNICAL FIELD

The apparatus and methods described below pertain to thermal processorsfor semiconductor wafers, and more particularly to an improvedsemiconductor processing furnace and methods of processing.

BACKGROUND OF THE INVENTION

In the thermal and chemical processing of semiconductor wafers, it ishighly desirable to very accurately control the thermal and gaseoustreatment to which the wafers are exposed during processing. Typically,batches of wafers are processed in a semiconductor processing furnacehaving an processing chamber which can be controllably enclosed. Theprocessing environment within the enclosed processing chamber iscarefully controlled to effect the desired processes.

Early designs for semiconductor diffusion processing furnaces wereconfigured with the wafer array and processing chamber in a horizontalorientation. This was apparently done in an attempt to obtain productshaving more uniform characteristics. However, the desired uniformity wasnot easily achieved and horizontal furnaces suffered some disadvantagesbecause of their configuration. In some furnaces it became difficult toachieve uniformity when performing high pressure oxidation or silicondeposition processes. These furnaces also proved difficult in achievingdesired quality levels for the wafer or other semiconductor articlesbeing processed.

In response to problems experienced by horizontal diffusion furnaces,alternative designs were developed. Furnaces having vertically arrangedwafer arrays and processing chambers were made in an effort to providebetter control of temperature and other processing parameters. U.S. Pat.No. 4,738,618 issued to Robert G. Massey et al. on Apr. 19, 1988 shows avertically oriented thermal processor having a vertically adjustablefurnace assembly and process tube. The process tube, constructed from aquartz bell jar, is vertically moveable in up and down directions withina supporting framework in conjunction with a likewise moveable furnaceassembly. Additionally, the furnace assembly and process tube aremoveable together between up and down positions, as well asindependently of one another. Heat is supplied to the thermal processorwhen the furnace assembly and process tube are both lowered into thedown position by controlling operation of heating elements within thefurnace assembly. To cool the process tube within the thermal processor,the operation of the heating elements is regulated such that interiorheat is dissipated to the exterior of the processor by convection.Although this vertical furnace design provided significant improvements,further improvements were found desirable to achieve greater temperatureuniformity and better control over other processing parameters.

One design challenge associated with the above vertical furnace designincluded a tendency for the thermal processor to collect deposits ofcontaminants on the inner surface of the quartz process tube undercertain treatment procedures. In an effort to address these problems,U.S. Pat. No. 5,000,682, issued to Donald W. Haight et al. on Mar. 19,1991 presented a vertical furnace design that separates the furnace intoa pre-heat and post-cool area in which the wafers are processed and inwhich gaseous or vapor treatments are conducted.

Another area of continuing design challenge is to more quickly cool thewafer array and processing chamber after high temperature thermalprocessing has been completed. Rapid cooling needs to be done in auniform manner to help minimize the risks of processing variationsbetween wafers and between different batches of wafers.

Relatively rapid but uniform cooling is also desired in order tominimize overall thermal exposure. Thermal exposure can have deleteriouseffects upon layers of the semiconductor article which have beenpreviously processed. This is widely recognized by the term thermalbudget which indicates that a wafer has a budget for the degree ofexposure to elevated temperature processes. The effects are not linearwith temperature, but instead have increasingly significant effects withhigher temperatures. Examples of deleterious effects associated withadded high temperature exposure include temperature induced crystaldefects or deviations, and undesired additional diffusion of dopants orother materials within the matrix of the semiconductor article beingprocessed. Thus it is desirable to bring a batch of wafers beingprocessed within a furnace up to a desired processing temperaturerelatively rapidly, and to cool the wafers also in a relatively rapidmanner. These goals are further emphasized because overall processingtime and costs can be reduced if the processing time can be reduced.

Another challenge in the design of semiconductor thermal processors iswith regard to more quickly achieving a desired temperature environmentwithin the process chamber so that wafers or other semiconductorarticles are heated at uniform rates and to uniform temperatures. Thedesired uniformity is variable in both axial and radial directionsrelative to the array of wafers being processed. Particularly, there isa need to realize a desired, or pre-defined thermal processing model inthe processing chamber during a processing step in order to produceprocessed wafers having better uniformity. Particularly, problems can beencountered due to axial and radial variations in temperature betweendifferent regions of the processing chamber. The ability to controlthese variations becomes more difficult as faster thermal ramp-up andramp-down targets are attempted in the process chamber. Therefore,improvements in furnace design are necessary in order to achieve anaggressive reduction in cycle time without a degradation in uniformityof processed wafers. The arrangement of heating elements and coolingfluids used in and around the processing chamber creates a delay inthermal response of the process chamber temperature which makes accuratedynamic control of the temperature during ramp-up, ramp-down andchanging temperature rate conditions particularly difficult.

A further problem posed by the use of presently available semiconductorvertical processing furnaces results when processing gases are exposedto non-inert furnace components within the process chamber. Typically,wafers must be processed in a controlled environment in order to preventundesirable oxidation. Ideally, the environment should be nearly inert.For example, inert gas is used during certain annealing processes.However, materials which are not completely inert and that are in fluidcontact with the processing gases can produce off-gassing of one or moreconstituents. Such off-gassing can introduce contaminants into theprocessing chamber which mix with processing gases. The high temperatureconditions and mixing of processing gases within the processing chambercan lead to introduction of such contaminants into the wafers of othersemiconductor articles being processed.

There is also a significant problem with regard to the handling ofsemiconductor processing waste streams. In the case of semiconductorfurnaces, the processing chambers are typically supplied with variousgases during thermal processing. Since processing pressures aretypically atmospheric or subatmospheric, the flow of processing gasesinto the processing chamber requires an approximate flow of spent gasesfrom the processing chamber. These spent processing gases are typicallyat relatively high temperatures which cause problems in handling anddisposal. Thus there is a need for thermal processors having improvedwaste stream outflows which can be more easily handled.

These and other considerations have led to the improved designs andprocesses described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the invention is illustrated in theaccompanying drawings which are briefly described below.

FIG. 1 is a perspective view of a preferred vertical thermal processoraccording to this invention.

FIG. 2 is a perspective view showing the processor of FIG. 1 with someportions broken away and removed to reveal internal components of thesystem.

FIG. 3 is a sectional view showing an upper portion of a furnace heaterassembly portion forming part of the thermal processor of FIG. 1.

FIG. 4 is a sectional view showing a lower portion of the furnace heaterassembly portion which complements the contents of FIG. 3.

FIG. 5 is a plan view of a top of a heating enclosure subassemblyforming part of the heater assembly shown in FIGS. 3 and 4.

FIG. 6 is a bottom view of a top portion of the heating enclosuresubassembly shown in FIG. 5.

FIG. 7 is a sectional view of the top portion taken along line 7--7 ofFIG. 5.

FIG. 8 is a bottom plan view of the bottom of the heating enclosuresubassembly.

FIG. 9 is a sectional view taken along the line 9--9 of FIG. 8.

FIG. 10 is an enlarged partial sectional view showing portions of thebase plate assembly and pedestal assembly shown in FIG. 4.

FIG. 10A is an enlarged detail sectional view taken from the encircledregion of FIG. 10.

FIG. 11 is a top plan view of a base support portion forming part of thebase plate assembly shown in FIG. 10.

FIG. 12 is a bottom view of the base support portion shown in FIG. 11.

FIG. 13 is an enlarged sectional view taken along the line 13--13 ofFIG. 11.

FIG. 14 is an enlarged partial sectional view taken along the line14--14 of FIG. 12.

FIG. 15 is an enlarged partial sectional view taken along the line15--15 in FIG. 11.

FIG. 16 is an enlarged plan view of an air distribution disk shown inFIG. 10.

FIG. 17 is a sectional view taken along the line 17--17 of FIG. 12. Thecutting plane of FIG. 17 is also shown in FIG. 16 with regard to how itcuts through the air distribution disk.

FIG. 18 is a bottom view of the air distribution disk shown in FIG. 16.

FIG. 19 is a perspective view of portions of the base plate assemblyshown in FIG. 10.

FIG. 20 is a perspective view of the outflow inner liner shown in FIG.10.

FIG. 21 is an exploded perspective view of a baffle array shown is FIG.10.

FIG. 22 is an enlarged perspective view of the pedestal assembly shownin FIG. 10.

FIG. 23 is a block diagram showing a preferred furnace control systemused in the thermal processor of FIG. 1.

FIG. 24 is a block diagram of a preferred furnace power controller usedin the thermal processor of FIG. 1.

FIG. 25 is a block diagram illustrating power switching circuitry usedin the power controller of FIG. 24.

FIG. 26 is a trigger circuit block diagram illustrating triggercircuitry used in the power controller of FIG. 24.

FIG. 27 is a clock generator block diagram illustrating clock generatorcircuitry used in the power controller of FIG. 24.

FIG. 28 is a power measurement circuit block diagram illustrating powermeasurement circuitry used in the power controller of FIG. 24.

FIG. 29 is an analog/digital converter block diagram illustratingintegrating charge balance converter circuitry used in the powercontroller of FIG. 24.

FIG. 30 is a schematic block diagram showing a general controller andfunctional relationships with components of the thermal processor ofFIG. 1.

FIG. 31 is a preferred outflow piping arrangement used with the outflowcooler shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

                  TABLE 1    ______________________________________    Listing of Subsections of Detailed Description and    Pertinent Items with Reference Numerals and Page Numbers    ______________________________________    Thermal Processor Generally                    13    Processing Boat  18    vertical thermal processor 10                    13    processing boat 12                                           18    front 1         13    processing boat base 23                                           18    back 2          13    upright standards 19                                           18    first side 3    13    notches 21       19    second side 4   13    Processing Head Assembly                                           19    top 5           13    head assembly or head 25                                           19    bottom 6        13    processing tube or jar 18                                           19    exterior surface panels 7                    14    furnace heater assembly 22                                           19    structural framework 24                    14    Processing Head Support and                                           20    access door 9   14    Actuation    loading chamber 11                    14    head assembly suspension                                           20    internal partitions 11a                    14    plate 131    front operator control panel 15                    15    head support framework 133                                           20    stop control 15a                    15    guide tracks 135 20    a run or start control 15b                    15    head support superstructure                                           21    indicator lights 15c and 15e                    15    frame portion 137    display and control input station                    15    guide track receiving channels                                           21    15d                   135a    tail section 42 15    head assembly actuators 28                                           21    Wafer Inventory 15    actuator rods 79 21    inventory stand 13                    16    Processing Vessel Assembly                                           22    upper support deck 13a                    16    processing chamber 16                                           22    lower support deck 13b                    16    processing tube or jar 18                                           22    wafer cassettes 17                    16    wall or shell 20 22    wafers 14       16    Processing Tube Lift                                           23    Wafer Transfer Mechanism                    16    Assembly    wafer transfer mechanism 48                    16    processing tube lift ring 30                                           23    engagement or contact head 47                    17    processing tube lift actuators                                           23    Pre-Load and Cooling Boats                    17    26    pre-load boat 54                    17    lift actuation rods 27                                           23    upright standards 49                    17    peripheral or outer lift ring 31                                           23    cooling boat 56 18    threaded fasteners 33                                           24    flange seal 41  24    detachable retainer pins 35                                           24    locator pin receptacles 47                    24    bottom flange 37 24    locator pins 43 24    flange retainer 39                                           24    locator pin keepers 648                    24    retainer fasteners 40                                           24    cooling fluid ports 45                    25    manifold connecting passages                                           34    annular distribution groove or                    25    134    channel 46            manifold chamber shields 135                                           34    cooling fluid passageway 89                    25    annular outer manifold                                           34    Furnace Heater Assembly                    25    chamber 137    Canister              exterior ports 124                                           34    furnace heater assembly 22                    25    central opening 141                                           35    canister 76     26    heating enclosure bottom ring                                           35    side wall or walls 77                    26    104    water jacket space 77a                    26    Furnace Heater Liner                                           35    canister top ring 119                    27    furnace liner 82 35    upper actuator mounting ring                    27    mounting flange 84                                           36    116                   liner mounting ring 86                                           36    bottom flange ring 80                    27    liner face seal 138                                           36    peripheral heat shield 32                    27    liner dome 83    36    Heating Enclosure Subassembly                    27    first cooling circuit connection                                           36    heating enclosure subassembly                    28    fitting 85    88                    first cooling circuit connection                                           36    circumferential segments 90-96                    28    conduit 122    end segment 100 28    Furnace Sensors  37    base segment 102                    28    temperature sensor arrays 128                                           37    electrical resistance heating                    28    sensor mounting apertures 132                                           37    elements 101          sensor receptacles 136                                           37    secondary insulation layer 98                    30    Base Plate Assembly                                           37    protective jacket or skin 103                    30    base plate assembly 168                                           37    end segment 100 30    main base plate member 160                                           38    lower face 104  30    base support member 162                                           38    annular recess 105                    30    fasteners 161    38    first or interior piece 106                    31    dowel pin 183    38    second or main piece 107                    31    base throat piece 164                                           38    third or outside piece 108                    31    main processing chamber seal                                           39    cooling fluid passageways 143                    31    172    interior ports 110                    31    first cooling fluid supply                                           40    second piece 108                    31    passage 89    annular inner manifold chamber                    32    supply fitting or tube 99                                           40    113                   annular coolant channel 208                                           40    manifold connecting passages                    32    connecting passages 207                                           41    114                   annular coolant channels 221                                           41    manifold chamber shields 115                    32    channel covers 223                                           41    annular outer manifold chamber                    32    dams 222         41    116                   peripheral recessed shoulder                                           42    exterior ports 120                    32    231    heating element conection                    32    seal retainer 232                                           42    terminals 140-152     retainer cap piece 234                                           42    handles 129     33    seals 235 and 236                                           42    end segment centeral apertures                    33    annular flow distribution                                           42    109                   space 237    heater base 102 33    coolant supply passageway                                           43    first part 123  33    238    second part 125 33    coolant supply line 239                                           43    third part 127  33    annular main seal space 243                                           43    fourth part 129 33    and is passed through a    annular recess groove 133                    33    main seal coolant outflow                                           43    cooling fluid interior ports 111                    34    passageway    annular inner manifold chamber                    34    244 and associated    126                   coolant outflow conduit 245                                           43    support port 190                    44    accessory fittings 174                                           43    ports 184 and 190                    44    gas delivery tube 176                                           43    recessed regions 191                    45    profile thermocouple arrays                                           43    cooling air distribution disk 196                    45    180    fasteners 193   45    O-ring seal 182  44    apertures 194   45    port 184         44    central aperture 201                    45    outlet 351       50    cooling supply port 198                    45    exterior ports 120                                           51    annular distribution cavity 216                    45    annular manifold chamber 118                                           51    exhaust ports 199                    45    ports 110        51    beveled O-ring seat 200                    45    passageways 111  51    base cooling cavity 170                    46    annular chamber 126                                           51    exit duct 251   46    side ports 124   51    exit duct end piece 253                    46    riser ducts 139  51    fasteners 254   46    Process Chamber Outflow                                           51    seal 261        46    top baffle 501   51    seal 269        46    second or intermediate baffle                                           52    cooling gas ports 262                    46    503    distribution channel 263                    46    central aperture 504                                           52    cover 264       46    spacers 505      52    cooling channel 255                    46    third or bottom baffle 508                                           52    cooling channel cover 256                    46    peripheral openings or notches                                           52    exit duct bottom flange 257                    47    509    J-hook fasteners 258                    47    peripheral spokes or lugs 510                                           52    outflow main seal 259                    47    inner liner 520  52    outflow seal heat shield 607                    47    top peripheral flange 521                                           52    Pedestal Assembly                    47    entrance or mouth 522                                           52    pedestal assembly 163                    47    exit or discharge 527                                           52    pedestal collar 271                    47    upper portion 523                                           52    accessory apertures 272                    47    lower portion 524                                           52    shoulder 273    47    Processing Chamber Outflow                                           53    pedestal cylinder 281                    48    Cooler    pedestal headpiece 283                    48    outflow cooler 600                                           53    pedestal holes 284                    48    outflow cooler sleeve or                                           53    locaing projections 336                    48    casing 602    central recessed area 286                    48    casing top flange 604                                           53    Fluid Cooling Circuits                    49    discharge port 609                                           54    first or inner fluid cooling circuit                    49    casing bottom shoulder 608                                           54    first flow path 75                    49    outflow cooler lining 605                                           54    second or outer fluid cooling                    49    coupling head or flange 606                                           54    circuit               flow diverter 630                                           55    second flow path 77                    49    top end 631      55    cooling fluid supplies 99                    49    bottom end wall 632                                           55    passageways 89  49    vent hole 635    55    annular chamber 46                    49    flow diverter feet 636                                           55    ports 45        49    bottom end wall 632                                           55    connection fitting 85                    49    tee 651          56    conduit 122     49    gas discharge line 653                                           56    flange 341      50    elevated section 654                                           56    spring-loaded gasket 342                    50    control valve 658                                           56    flow plenum 349 50    valve controller 659                                           56    high temperature packing 347                    50    purge fitting 660                                           56    flow mover 350  50    purge flow control valve 665                                           56    Furnace Power Controller                    61    liquids discharge branch 680                                           56    furnace power controller 350                    61    flush connector 681                                           56    model based controller 352                    61    flush control valve 683                                           57    control system 348                    62    flow indicator 684                                           57    power controller circuit 354                    63    gas trap 687     57    silicon controlled rectifiers                    63    Methods and Operation                                           57    (SCR) 392    microprocessor based host                    64    computer 356    serial communications link 358                    64    communication interface 360                    64    dedicated microprocessor 362                    64    pair of power measurement                    65    circuits 366 and 367    SCR trigger timing circuits 368                    65    and 370    separate power switch circuit                    66    372 and 374    PLL clock generator circuit 380                    66    A/D converter 386 and 388                    66    synchronous voltage to                    66    frequency (V-F) converter    390 and 392    metal oxide varistor (MOV) 394                    67    resistor/capacitor (RC) snubber                    67    396    diode steering logic circuitry 398                    67    phase locked loop circuit 400                    69    digital counter 402                    69    gating circuits 404                    69    high frequency voltage                    69    controlled oscillator (VCO) 406    zero cross detector at input line                    69    408    step down transformer 410                    70    current transformer 412                    70    analog multiplier 414                    70    voltage output along line 418                    71    analog input 420                    71    counter 422     71    latch 424       71    General Controller                    73    processing fluids control valves                    74    803    wafer transfer sub-controller 804                    74    Manner of Making                    74    ______________________________________     ***(End of Table 1)***

Thermal Processor Generally

FIG. 1 shows a preferred vertical thermal processor 10 according to thisinvention. Processor 10 has a front 1, back 2, first side 3, second side4, top 5, and bottom 6. FIG. 1 shows a number of exterior surface panels7 which are used to provide a general covering and improved appearanceof the overall machine when fully assembled. Surface panels 7 areattached to a structural framework 24 (shown in FIG. 2).

The front 1 of processor 10 includes an access door 9 which is mountedfor slidable action to allow access to a loading chamber 11 shown inFIG. 2. Access door 9 is moved into a retracted condition to allow ahuman operator to place wafers or other semiconductor articles into andremove them from the loading compartment 11. Loading compartment 11 isenclosed to protect the wafers against contamination and serves thefunctions of inventorying the wafers, holding the wafers in preparationfor loading into the processing chamber, and holding the wafers forfurther cooling after the wafers have been removed from the processingchamber.

FIG. 2 also shows that in order to further minimize contamination of thewafers and the introduction of contaminants into a processing chamber16, the loading chamber 11 is separated from other sections of thethermal processor by several internal partitions 11a. The loadingchamber is preferably supplied with highly filtered air or otherenvironmental gas to reduce contamination. The preferred filtered airsupply is not illustrated, but is contained above the loading chamber tothe left in FIG. 2.

FIG. 1 also shows the front operator control panel 15. Front operatorcontrol panel 15 is accessible from the cleanroom side of the thermalprocessor. As shown, control panel 15 includes a stop control 15a, a runor start control 15b, and a series of indicator lights 15c and 15e whichshow various operational states or conditions. The front operatorcontrol panel 15 also preferably includes a touch screen display andcontrol input station 15d which both displays information used by thehuman operator and allows the operator to input various information andmake selections concerning the desired processing recipe and otheroperational parameters. A rear or maintenance display (not shown) canadvantageously be included at the rear 2 of the thermal processor. Thisoptional maintenance display and control input station is available fromthe grey room side of the thermal processor.

The outer configuration and front face of the thermal processorfacilitates mounting in either single installations or in groups whereinmultiple processors 10 are arranged side by side. Maintenance isfacilitated by using a tail section 42 provided in a back portion of theprocessor. The tail section is of reduced width to allow maintenancepersonnel to access the back of the processor from the grey room side,thus facilitating maintenance and cleaning.

Wafer Inventory

Refer now to FIG. 2 which shows internal components of thermal processor10. At the front in FIG. 2 is an inventory in the form of an inventorystand 13. Inventory stand 13 can be of various constructions. As shownthe inventory stand is provided with two support levels in the form ofupper support deck 13a and lower support deck 13b. The inventory standholds a suitable number of wafer cassettes 17, such as the four shown.The wafer cassettes are preferably supported upon the inventory decks13a and 13b in a specific position such as by registration of thecassettes with registration features of the deck (not specificallyshown).

Each wafer incoming cassette is provided with wafers 14 which are readyfor thermal processing. Outgoing cassettes contain wafers which havealready been processed.

The inventory stand also serves as a product input-output section whichis typically loaded in a manual fashion by a human operator via door 9.Alternative means for loading and unloading can also be employed, suchas automated wafer handling equipment (not shown) which place the wafercassettes 17 in appropriate locations for processing.

Wafer Transfer Mechanism

Adjacent to the input-output section is a wafer transfer mechanism 48.Wafer transfer mechanism 48 can be of various types either custom madeor commercially available. The preferred wafer transfer mechanism has anengagement or contact head 47 which contacts the wafers. The engagementhead can advantageously include a vacuum port (not shown) which helpssecure a wafer in position upon the contact head. The preferred wafertransfer mechanism has the ability to rotate or pivot to assume variousangular positions, as well as to extend and retract laterally to achievedifferent degrees of radial extension relative to its central pivotaxis. The wafer transfer can also be controllably elevated to remove andreplace wafers from the cassettes 17 held in the input-output inventory13. Wafer transfer 48 also moves wafers to several other positionswithin the processor as will be explained further below.

Pre-Load and Cooling Boats

FIG. 2 further illustrates that processor 10 also includes a pre-loadboat 54 which receives wafers from the input-output inventory 13 viawafer transfer 48. Pre-load boat 54 is used to store a pre-load array ofwafers 14 in anticipation of movement of the wafers into the processingchamber which will be described more fully below. The pre-load boat ispreferably a stand formed of quartz or other suitable materials having aseries of receivers formed therein at spaced vertical positions. Thereceivers are advantageously formed by notches formed into uprightstandards 49. In the preferred construction there are three standardswhich form the pre-load boat 54. The wafer transfer 48 moves to thedesired vertical height position and moves the contact member 47 towardpre-load boat 54. The wafer transfer then installs the wafer onto orremoves the wafer from the pre-load boat depending upon whether thewafer is being loaded or unloaded therefrom.

FIG. 2 also shows a cooling boat 56 which is constructed substantiallythe same as the pre-load boat 54 just described. The cooling boatreceives wafers which have been thermally processed and are still atelevated temperatures. The wafers are positioned into the cooling boatto form a cooling boat array from which heat dissipates. This allows theprocessing chamber to be utilized for loading the next batch of wafersbeing processed even though the wafers are sufficiently hot that furthercooling is needed before they are placed in wafer carriers 17.

Processing Boat

FIG. 2 also shows a processing boat 12 which is vertically arranged tohold a processing array of wafers 14 or other semiconductor articlesbeing processed. The processing boat is positioned in a stationaryposition upon a pedestal assembly 163 and base plate assembly 168 bothof which will be described more fully below.

The processing boat includes a processing boat base 23 (see FIG. 3) anda plurality of upright standards 19 each of which has a series ofnotches 21 into which the wafers are received. This forms a verticalarray having a series of receivers which hold the wafers duringprocessing.

Wafers are loaded into and unloaded from the processing boat 12 usingthe wafer transfer 48 in a manner substantially the same as describedabove in connection with the loading and unloading of the pre-load boat54. Wafers are taken from the pre-load boat and moved by the wafertransfer to the processing boat. After processing, the processed wafersare moved by the wafer transfer to the cooling boat 56.

Processing Head Assembly

The thermal processor 10 includes a processing head assembly which isgenerally referred to as head assembly or head 25. The head assembly isdeployed from above. The head assembly includes a processing tube or jar18 which is preferably in a form similar to a bell jar. The processinghead assembly is constructed so as to allow the processing jar to moveupwardly and downwardly over the wafer array. When deployed downwardlythe processing jar covers the wafer array and seals against the baseplate assembly 168 to form a substantially enclosed processing chamber16.

The head assembly 25 also includes furnace heater assembly 22. Thefurnace heater assembly 22 is used to insulate and heat the array ofwafers held on the processing boat. The processing head assembly isconstructed to allow the furnace heater assembly to move upwardly anddownwardly. The heater assembly and processing jar are constructed toform a coaxial arrangement so that the processing jar can be receivedwithin the heater assembly 22.

Processing Head Support and Actuation

FIG. 2 shows that the head assembly 25 is advantageously suspended froma head support which advantageously includes head assembly suspensionplate 131. The suspension plate or piece 131 is connected to a headsupport framework 133 using detachable fasteners. The head supportframework 133 is mounted for movement to facilitate maintenance byallowing the head assembly to be moved to the back of the thermalprocessor. In particular, the head support framework 133 is movable tofacilitate changing of the processing tube 18 in a convenient manner atthe back of the processor. As shown, the support framework is mountedfor translational movement so as to allow movement frontwardly orrearwardly relative to the stationary frame 24 of the thermal processor.This is advantageously accomplished using a support carriage which isformed in-part by the support framework 133 and suspension plate 131.The support carriage also includes a plurality of rollers (notillustrated) which are guided by two complementary guide tracks 135mounted upon a head support superstructure frame portion 137 which formspart of the stationary frame 24 of the processor. The guide trackspreferably have guide track receiving channels 135a which receive therollers and restrain motion in either the up or down directions.Translational motion of the support carriage within a defined range ofthe guide tracks is allowed. The frame 24 is constructed to allowmovement of the head assembly rearward when the head assembly is in anup position. The head assembly can then be moved toward the backportions of the machine and accessed adjacent to the tail section 42 formaintenance.

The head assembly 25 is advantageously suspended from the support plateor piece 131 using head assembly actuators 28. Head assembly actuators28 have main parts which are carried with the canister 76 describedbelow. Actuators 28 also have extendible and retractable actuator rods79 (FIG. 3) with upper, distal ends. The distal ends are securelyfastened to the support plate 131. When actuators 28 are extended, thehead assembly moves downwardly to lower the furnace heater about theprocessing chamber for thermal processing. Lift actuators 28 can be ofvarious types. One preferred construction uses pneumatically poweredrams. Alternative actuators, such as electrically powered mechanicalscrew actuators may alternatively be possible.

Processing Vessel Assembly

The processing boat 12 is positioned so as to be within processingchamber 16 when processing is taking place. The processing chamber isbecomes enclosed when the processing tube or jar 18 is moved downwardlyand over the processing boat to cover the processing array. In FIG. 2the processing tube assembly is shown moved partially downward into anintermediate position which is between its up and down positions.

Process tube or jar 18 is advantageously formed in a shape similar to abell jar with a wall or shell 20 that has an inner surface which definesmuch of the perimeter of the processing chamber 16. The process jar alsohas an outer surface. The process jar is preferably made from quartz.

The lower reaches of the processing chamber are defined by portions of abase plate assembly 168. The processing jar 18 is mounted for verticalmovement to allow the processing array to be opened into an openposition for installation and removal of wafers, or to be closed into aclosed position to form a substantially enclosed processing chamber usedduring thermal processing. When joined, the processing jar and baseplate assembly form a substantially enclosed processing vessel. Theseparts are joined when the processing jar is lowered and placed in sealedrelationship with the base plate assembly. The processing chamber 16 iscontained and substantially enclosed within the processing vessel whenthe processing vessel is in such a closed condition.

Processing Tube Lift Assembly

The processing tube or jar 18 is supported upon a processing tube liftring 30. Lift ring 30 forms part of a lift ring assembly which ismovably mounted so as to allow vertical motion between up and downpositions. FIGS. 4 and 10 show key portions of the lift ring assembly.The processing tube lift ring 30 is connected to and supported by a setof processing tube lift actuators 26. The upper ends and main portionsof the lift actuators are secured to upper portions of a canisterassembly 76 which is described in greater detail below. Lift actuators26 also include extendible and retractable lift actuation rods 27. Inthe preferred construction there are three actuators each with actuationrods 27 which are controllably extendible relative to the main portionthe actuators. Lift actuators 26 can be of various types. One preferredconstruction uses pneumatically powered rams. Alternative actuators,such as electrically powered mechanical screw actuators mayalternatively be possible.

The distal, lower ends of actuation rods 27 are securely connected tolift ring 30. This is preferably done using an intermediary structure inthe form of a peripheral or outer lift ring 31 (see FIG. 4). Theactuation rods are preferably positioned through apertures in the outerlift ring and secured using detachable fasteners, such as threadedfasteners 33. The lift ring 30 is secured to the outer lift ring 31 toform a lift ring assembly using a plurality of detachable retainer pins35 which engage these parts at several locations and are installed aboutthe periphery of the outer lift ring 31. Although a two-part ringconstruction is shown for the lift ring assembly, other alternativeconstructions are possible.

FIG. 10 further shows that the processing tube 18 is provided with abottom flange 37. Bottom flange 37 rests upon a shoulder formed alongthe inner periphery of a central aperture formed in the lift ring toreceive the bottom portions of the processing tube. A flange retainer 39bears upon the upper face of the processing tube flange. The flangeretainer is connected by retainer fasteners 40 to the lift ring 30 todetachably secure the processing tube to the lift ring assembly. Aflange seal 41 is advantageously included between the flange 37, flangeretainer 39, and lift ring 30. Additional seals or pads (notillustrated) can also advantageously be included between the upper andlower faces of the flange and the adjacent ring 30 or retainer 39.

FIG. 10 also shows that the lift ring assembly is advantageouslyprovided with one or more locator pin receptacles 47. Receptacles 47receive locator pins 43 which are secured in the upper face of the baseplate main piece 160 using locator pin keepers 648. The locator pinscause the lift ring assembly to align and be mated with the base plateassembly in precise horizontal registration when the lift ring assemblyis lowered into the down position.

FIG. 10 further shows that lift ring 30 is provided with a plurality ofcooling fluid ports 45 which are formed at numerous positions about thelift ring to form a circular array, such as containing 20-30 ports. Thepassageways 45 allow a circumferentially distributed supply of coolingair to pass therethrough as part of a first fluid cooling circuit whichwill be described in greater detail below. Adjacent to the passagewaysis an annular distribution groove or channel 46 which allows cooling gasto be distributed to the individual passageways 45 about the channel.Channel 46 is in fluid communication with a cooling fluid passageway 89in the base plate main member 160. Heat is transferred to the air orother cooling fluid from the adjacent mounting ring 30 and the area nearprocessing tube bottom flange 37. This construction helps to cooladjacent portions of the processing tube 18 and its supporting lift ringassembly. The cooling fluid also proceeds upward to cool other parts ofthe processing tube.

Furnace Heater Assembly Canister

FIGS. 2, 3 and 4 show the furnace heater assembly 22. As FIG. 2indicates, the furnace heater assembly is part of the head assembly andis mounted above the processing boat 12 and processing tube 18. Furnaceheater 22 is preferably mounted for vertical motion in a manner whichparallels the motion of the processing tube lift assembly describedabove. Both the furnace heater assembly and processing tube assembly aremoved upwardly when the processing boat 12 is being loaded. FIG. 2 showsthe furnace heater positioned fully upward into a retracted or upposition. Prior to processing, the processing tube assembly and furnaceheater assembly are moved downwardly. The furnace heater is moved intoan extended or down position wherein the heater assembly surrounds mostof the processing tube 18 and supplies heat to the processing tube andthe processing chamber enclosed therein.

In the preferred construction shown, the heater assembly can be raisedand lowered independently from the processing tube assembly, once theprocessing tube assembly has been lowered into the down position.

The outer portions of furnace heater assembly 22 includes a protectivecanister 76. The preferred canister 76 includes a side wall or walls 77.As shown best in FIGS. 3 and 4, the side wall is preferably made using adouble wall construction with a canister cooling system formed therein.The preferred canister cooling system includes a water jacket space 77acontained between the inner and outer canister walls 77. Water iscirculated through the canister water jacket space to cool the canisterand its surfaces against the high temperatures generated in the furnaceheater by the heating enclosure subassembly described below. Water canbe circulated through space 77a via fittings (not shown) using apressurized water supply (not shown).

The canister also preferably includes a series of lateral wallreinforcing rings 78. Reinforcing rings 78 extend circumferentiallyabout the inner side wall of the canister for added structural support.

Canister 76 further includes a canister top ring 119 which is fastenedto the top portions of side wall 77. The canister top ring 119 is usedto mount an upper actuator mounting ring 116. The actuator mounting ring116 is used to mount the upper ends of actuators 26 and 28.

FIG. 4 shows that canister 76 also includes a bottom flange ring 80fastened to a bottom edge of the canister assembly. Bottom flange 80 isused to mount the lower ends of actuators 26 and 28. Flange 80 is alsoused to mount a peripheral heat shield 32 which extends about the bottomcircumference of the canister assembly to shield heat radiated from theouter lift ring 31 and adjacent parts of the head and base plateassemblies.

The top plate, top ring, flange ring, side wall, heat shield and otherparts of the canister assembly are advantageously made from stainlesssteel or other suitable materials.

Heating Enclosure Subassembly

FIGS. 3 and 4 further show that the furnace heater assembly 22 includesa heating enclosure subassembly 88 which heats and insulates theprocessing vessel and processing chamber during processing. The heatingenclosure subassembly 88 is mounted within canister 76. The canisterassembly, heating enclosure subassembly, and heater liner 82 togetherform the principal components of the heater assembly 22.

The heating enclosure subassembly includes a plurality of segments whichare assembled together to form a heating enclosure wall or walls. In thepreferred construction, the segments include a plurality ofcircumferential segments 90-96, end segment 100, and a base segment 102.Electrical resistance heating elements are advantageously included inthe circumferential segments 90-96 and in the end segment 100. Endsegment 100 and base segment 102 are specially constructed to providefor the passage of cooling fluid therethrough in a manner which reducesradiant heat loss from the interior chamber of the heating or furnaceenclosure.

Segments 90-96 and 100 include both an electrical resistance heatingelement and surrounding insulatory and structural materials. Theelectrical resistance heating elements 101 are positioned along theinterior face of the segments and formed in a sinuous pattern, such asshown for the top heating element 101 of FIG. 6. Heating elements 101are preferably formed from a powdered metallurgical material havingdesired electrical resistance properties. The preferred electricalresistance heating elements include a powdered metallurgical mixtureincluding chromium, aluminum, iron, and yttrium. The proportions ofthese materials can vary as is known in the art of producing suchpowdered metallurgical electrical resistance heating elements. Theheating elements are shaped into convoluted patterns which preferablyprovide a heat flux density of approximately 20-30 watts per square inchof effective heating surface along the interior surface of the heatingelement segments 90-96 and 101. Even more preferably the heat fluxdensity is about 28 watts per square inch. The preferred heatingelements can have a conductive element having a diameter ofapproximately 2-3 millimeters, more preferably 2.2 millimeters.

The electrical resistance heating elements are preferably trained into aserpentine pattern to provide relatively uniform heat flux from theinner surface of the segment. Each element is advantageously affixed toeach segment by a plurality of retaining clips (not shown) that aresecured to the inner surface with fasteners.

The heating enclosure segments 90-96, 101 and 102 preferably includeceramic fiber materials which can be suitably molded or otherwise shapedto the desired shapes. More preferably, the ceramic fiber materials canbe made of approximately 50% alumina fibers and 50% silica fibers. Otherformulations and types of materials may also be satisfactory.

The circumferential heating element segments 90-96 are arranged into alongitudinal heating element array with adjacent elements inlongitudinal juxtaposition. The array of heating element segments issurrounded by a secondary insulation layer 98. Secondary layer 98 isformed of a highly insulatory material, such as fibered ceramic materialindicated above or other types of ceramic fibers which are mattedtogether to form a relatively less dense layer having good thermalinsulation properties. The secondary layer 98 is preferably a continuouslayer formed about the exterior of segments 90-96. The outer surface ofinsulatory layer 98 is advantageously encased in a protective jacket orskin 103 of stainless steel sheet metal or other suitable materials thatcan be welded or otherwise joined to adjacent parts of the heatingenclosure assembly along mating surfaces.

FIGS. 6 and 7 show the preferred construction for end segment 100 ingreater detail. End segment 100 is secured to the top of the array ofcircumferential segments 90-96, such as by using a suitable bondingagent which bonds the segments together, and/or by securing themtogether with the protective jacket 103. As shown, the lower face 104 ofsegment 100 is provided with an annular recess 105 which receives theupper portion of the adjacent circumferential segment 90.

FIG. 6 also shows heating element 101 which is mounted upon the insideface of the end segment. The end heating element is used to provideuniform heating and added control relative to wafers supported by theupper portions of the processing boat 12. Other aspects of the heatingelement are described above.

FIGS. 6 and 7 indicate that end segment 100 is preferably fabricatedusing three pieces of the molded ceramic fiber material, such asdescribed above. The three piece assembly includes a first or interiorpiece 106, a second or main piece 107, and a third or outside piece 108.These pieces are specially configured to form a plurality of coolingfluid passageways 143 formed therein. The cooling fluid passageways 143form part of the second fluid circuit described farther below.

The first or interior piece 106 is adjacent the furnace heating chamberand mounts the heating element 101. Interior piece 106 includes aplurality of interior ports 110 which are in direct fluid communicationwith the interior chamber of the heating enclosure subassembly. Asshown, there are thirty two ports 110 which are arranged in a circularcooling fluid port array at approximately equal radial positions and atapproximately regularly spaced angular positions. The ports arepositioned radially so as to be near but inward a short distance fromthe interior surface defined by the heating element segments 90-96. Itis alternatively possible to use other configurations and spacing forports 110.

FIGS. 6 and 7 also include a second piece 108 which forms part of endsegment 100. The lower face of second piece 108 includes an annularinner manifold chamber 113. The inner manifold chamber is in fluidcommunication with the internal ports 110. Outwardly adjacent to theinner manifold chamber 113 is a series of manifold connecting passages114. The manifold connecting passages are defined by a plurality ofmanifold chamber shields 115. The manifold chamber shields 115 areformed as downward extensions of the second piece 108 as illustrated inFIG. 7. Outwardly from passages 114 and shields 115 is an annular outermanifold chamber 116. Outer manifold chamber 116 is in fluidcommunication with passages 114 and a suitable number of exterior ports120. Exterior ports 120 are in fluid communication with the space whichis outside of the heating element assembly 88. Exterior ports 120 canextend out the side as shown, or alternatively out the top of the heaterenclosure (not shown).

The construction just described provides a convoluted flow passagewaywhich substantially reduces radiant heat losses which occur as comparedto having a straight port arrangement. The shields 115 are incoordinated proximity to the ports 110 to reflect radiant energy beamedthrough ports 110 from the furnace heating chamber. The passages alsotemper the air to some degree before entry into the heating chamber.

The heating elements 90-96 and 101 are electrically connected to a powersupply system via heating element connection terminals 140-152 andassociated wiring (not shown). The preferred power supply system isdescribed below in greater detail. End segment 100 can also beoptionally provided with handles 129.

The end segment 100 is also provided with end segment central apertures109. Central apertures 109 allow a first cooling circuit connectionconduit 122 to extend therethrough and mate with a first cooling circuitconnection fitting 85 formed upon the furnace liner 82.

The heating enclosure subassembly 88 also includes a heater base 102which is shown in isolation in FIGS. 8 and 9. Base 102 is affixed to thebottom of the assembled stack of heating element segments 90-96. Thepreferred base shown is advantageously constructed by assembling fourparts. As shown, base 102 is formed by joining together a first part123, a second part 125, a third part 127, and a fourth part 129. Theseparts are preferably molded or otherwise formed prior to assembly andthereafter joined together in a suitable fashion such as by bonding witha suitable bonding agent for the type of insulatory material used. Inthe preferred form these parts are molded from ceramic fiber materialsas explained above. Alternative constructions are also possible.

The first part 123 includes an annular recess groove 133 which receivesthe lower edge of the bottom segment 96. The bottom segment can bebonded or mechanically retained in the groove 133 in a fashion similarto the joint between the top segment 90 and groove 105.

The first part 123 and fourth part 129 define a plurality of coolingfluid interior ports 111 formed through the base in a suitable fashion.As shown, ports 111 are in a circular array open along the top face ofthe base and preferably at regularly spaced angular positions about thecentral opening 123. As shown, there are thirty two ports 111 atequiangularly spaced positions. Ports 111 form parts of a second coolingcircuit which will be more fully described below. Ports 111 arepreferably in fluid communication with the interior chamber of thefurnace heater and in fluid communication with an annular inner manifoldchamber 126 positioned beneath the ports. FIG. 8 shows a series ofmanifold connecting passages 134. The manifold connecting passages aredefined by a plurality of manifold chamber shields 135. The manifoldchamber shields 135 are formed as upward extensions of the third part127. Outwardly from passages 134 and shields 135 is an annular outermanifold chamber 137. Outer manifold chamber 137 is in fluidcommunication with passages 134 and a suitable number of exterior ports124. Exterior ports 124 are in fluid communication with riser ducts 139shown in FIGS. 4 and 10.

The construction just described provides a convoluted flow passagewaywhich substantially reduces radiant heat losses which occur as comparedto having a straight port arrangement. The shields 135 are incoordinated proximity to the ports 111 to reflect radiant energy beamedthrough ports 111 from the furnace heating chamber. This constructionalso allows cooling fluid to be passed through passageways 111, 126,134, 137, ports 124 and riser ducts 139 as part of the second fluidcircuit described more fully below.

Base 102 also includes a central opening 141 within which is receivedfurnace liner 82 and processing jar 18. The heating enclosuresubassembly is preferably mounted in coaxial alignment within thecanister 76 by using a heating enclosure bottom ring 104 that isconnected to the bottom of base 102. The bottom ring is fastened orotherwise suitably attached to the canister flange ring 80. FIGS. 8 and9 show that most preferably, the positioning ring 104 is formed from apiece of metal having an inner edge which is connected to the base.Fasteners extend through receiving holes formed through the ring andmounting blocks and are threaded into complementary receptacles formedin the canister flange ring 80.

Furnace Heater Liner

As best shown in FIGS. 3, 4 and 10, a furnace liner 82 is included alongthe inside of the heating enclosure assembly 88. The liner 82 forms aninner wall of the furnace heater. The liner is preferably constructed ina shape and size which is complementary to the processing tube 18. Asshown, the inner surface of the liner is spaced apart in approximatelycoaxial relationship with an outer surface of the process tube 18. Thefurnace liner is also shaped in a bell jar shape which is larger butsimilar to the bell jar shape of the processing tube 18.

Furnace liner 82 further has a bottom opening that allows the liner topass over the processing tube 18 as the furnace heater assembly islowered thereover. The lower end of the furnace liner also flaresoutwardly to provide a mounting flange 84. The furnace liner 82 ismounted to remaining portions of the furnace heater assembly and held incentered coaxial alignment within the interior of the furnace. This isadvantageously accomplished by capturing the mounting flange 84 betweenthe canister flange ring 80 and a liner mounting ring 86. The linermounting ring is brought into engagement with a bottom face of thecanister flange ring, thereafter the liner mounting ring is secured tothe canister flange ring by a plurality of fasteners. A first liner sealis provided along the peripheral edge of the flange 84. A liner faceseal 138 is provided between the lower face of mounting ring 86 to sealagainst the upper face of the lift ring 30 forming part of theprocessing tube assembly.

FIG. 3 shows that the top end of liner 82 preferably includes a linerdome 83. Centrally located on the dome is an first cooling circuitconnection fitting 85 which is preferably integrally formed withremaining portions of the dome. A first cooling circuit connectionconduit 122 seals with fitting 85 to form part of the first fluidcooling circuit.

The furnace liner 82 is preferably constructed of quartz and is mostpreferably fabricated as a singular piece having the features describedabove.

Furnace Sensors

A plurality of temperature sensors, such as thermocouples, are mountedin the furnace 22 in order to provide an indication of the temperaturesbeing developed by the heating elements contained in segments 90-96 and101. As shown, there are two groups of spike temperature sensors whichare provided as temperature sensor arrays 128. The spike thermocouplearrays are positioned in the cavity adjacent to the heating elements,which is between the heating enclosure subassembly 88 and the furnaceliner 82. The spike thermocouple arrays 128 are mounted through sensormounting apertures 132 formed through end assembly 100. The lower endsof sensor arrays 128 are supported in base 102 at sensor receptacles136.

Additional profile temperature sensors are mounted upon the base plateassembly 168 and such are described below in connection with thedescription of that assembly.

Base Plate Assembly

The thermal processor 10 also includes a base plate assembly 168 whichis supported upon portions of the stationary framework 24. The baseplate assembly remains in a stationary position throughout processing.The base plate assembly supports a pedestal assembly 163 which in turnsupports the processing boat 12 and any wafers 14 held thereon. Thepreferred construction of the pedestal assembly 163 is considered belowafter the base plate assembly 168 is described.

FIG. 10 shows that the base plate assembly is preferably constructedusing three principal pieces. One principal component is a main baseplate member 160 which is secured to and supported upon the frame 24.Main base plate member 160 is provided with a plurality of mountingapertures 216 which are used to secure the member to the frame 24.

A second principal part is the base support member 162 which isconnected to the underside of main base plate member 160 using fasteners161. A dowel pin 183 can be used at one or more points to assureaccurate positioning of the member 162 relative to main base platemember 160.

The support member 162 is positioned beneath the third principal piecewhich is a base throat piece 164 which is supported thereon. The basethroat piece 164 is supported laterally by the inner edge of the mainbase plate 160.

The main base plate 160 and support member 162 are preferably made ofstainless steel and serve important functions as structural members. Thebase throat piece 164 is exposed to high temperatures and processinggases contained within the processing chamber 16. Because of suchservice, the base throat piece 164 is preferably made from quartz orother suitable material which is capable of high temperatures. Thethroat piece 164 also must perform without off-gassing undesirableconstituents or otherwise reacting in the severe environment of theprocessing chamber. The base throat piece 164 also serves to shield themain base plate 160 and support member 162 from exposure to theprocessing gases contained within the processing chamber. Thisarrangement has the advantage that substantially the entire surface ofthe base plate assembly which is in adjoining fluid communication withthe processing chamber 16 is formed from quartz material, therebyeliminating potential adverse effects of off-gassing from metalcomponents which might contaminate the processing chamber 16.

Another important part connected to the base plate assembly is a mainprocessing chamber seal 172. In the construction shown, the mainprocessing chamber seal 172 is supported upon the base throat piece 164.Main processing chamber seal 172 seals between the quartz throat piece164 and the bottom end of processing tube 18. The placement of the sealbetween these parts provides almost total quartz material being used toconfine the lower portions of the processing chamber.

The base plate assembly is provided with features designed to cool themain seal 172. A main seal cooling gas distribution system is providedto provide cooling gas, such as air or nitrogen, at ambient temperaturesto the seal area. The main seal cooling gas distribution system isdescribed more fully below after first considering some additionfeatures and construction of the base plate assembly.

The main base plate member 160 is provided with a number of featureswhich allow for sealing and delivery or passage of fluids. One keyfeature is a pair of circular upper face seals 203. Face seals 203 canadvantageously be made of Viton elastomer. Face seals 203 extend aboutthe greater diameter of the upper face of the main base plate member 160to define an annular sealed area against the lower face of thevertically movable processing tube assembly. When the processing tubeassembly moves downwardly, then seals 203 are engaged by the lower faceof processing tube lift ring 30. The annular sealed area between seals203 is used to seal annular channel 46 formed in the lower face of liftring 30. Cooling fluid passing through the first cooling circuit issupplied to the annular channel 46 via a first cooling fluid supplypassage 89 formed through main base plate member 160. Supply passage 89is advantageously connected to a supply fitting or tube 99 which extendsbelow the main base plate member and is connected to a suitable sourceof cooling fluid.

Main base plate member 160 is also preferably provided with a coolingsystem in the form of an annular coolant channel 208. Channel 208 isformed in the upper face of the main base plate member. It is providedwith a coolant channel cover piece (not shown due to scale of drawing)which serves to contain water or other suitable coolant within thechannel. The channel and cover are preferably constructed so that afluid path is formed which extends substantially around the entirecircumference, but not entirely around. This is most advantageouslyaccomplished by forming channel 208 most of the way about thecircumference, but by leaving a small dam (not shown) across thechannel. Coolant is then introduced into the channel on one side of thedam and then circulated around the channel to flow out of the channel onthe other side of the dam. Coolant is supplied to channel 208 in anysuitable fashion, such as by connecting passages 207 shown schematicallyin FIG. 10.

A similar cooling arrangement is also used to cool the base supportpiece 162. FIG. 12 shows in greater detail a series of three parallelannular coolant channels 221. Channels 221 have channel covers 223 whichcover the channels and allow them to serve as substantially enclosedcoolant passageways. FIG. 14 shows that along section line 14--14 thereare dams 222. Dams 222 can either be part of the basic structure ofpiece 162 or inserts. Coolant is introduced into a port 224 and flowsabout the channel to flow from the complementary port 224 on theopposite side of dams 222. This arrangement allows large amounts of heatto be removed from the support piece 162 by circulating water or othersuitable coolant through the channels.

The support piece 162 and main base plate member 160 also are adapted toprovide a cooling flow of air, nitrogen or other suitable coolant fluidto the main processing chamber seal 172. This is preferably done in aconstruction which distributes the cooling air about the entire annularseal. FIG. 10A shows the preferred construction in enlargedcross-section detail. Seal 172 is advantageously a P-shaped seal whenviewed in cross-section. The high temperature service requires asuitable high temperature seal material to be used. A preferred materialis DuPont Kalrez, although other high temperature seal materials arealternatively possible.

FIG. 10A shows that seal 172 is securely mounted upon the upper surfaceof the quartz throat piece 164. This is advantageously done along aperipheral recessed shoulder 231 of throat piece 164. A seal retainer232 bears upon a flange portion of the P-shaped seal 172 to retain theseal in position. Retainer 232 is secured to the main base plate piece160 using fasteners (not shown) which extend through the overlyingretainer cap piece 234. Between the retainer 232 and retainer cap piece234 are two additional seals 235 and 236 which seal between these parts.An annular flow distribution space 237 is defined between the seals 235and 236 and between the retainer and retainer cap. Air, nitrogen, orother suitable cooling fluid is supplied to the flow distribution space237 via a coolant supply passageway 238. A coolant supply line 239supplies coolant to the passageway and distribution space 237. Retainer232 is provided with coolant release ports 240 which communicate thecoolant from distribution space 237 toward the seal 172. The coolantflowing from ports 240 is preferably directed at the seal and then flowsabout the seal to reduce the temperature of the seal. The coolant thenflows about an annular main seal space 243 and is passed through a mainseal coolant outflow passageway 244 and associated coolant outflowconduit 245.

The support piece 162 is also preferably provided with a means formounting a plurality of attachments or accessories which extend into theprocess chamber 16. The embodiment shown has been provided with fiveseparate accessory fittings 174. Accessory fittings 174 are constructedsimilarly but can be used for various purposes. One or more of fittingsare used to mount a gas delivery tube 176 (partially shown in FIG. 3)which has an open discharge end near the top of the processing chamberand extends down along the side of the processing boat 12. Tube 176allows various processing chemicals to be introduced into the processchamber. Another regular use of one or more of fittings 174 is to mountone or more profile thermocouple arrays 180. The preferred profiletemperature sensor arrays 180 extend upwardly into the processingchamber 16 between the processing tube 18 and the wafer boat 12.Preferably, the gas delivery tube 176 is formed from quartz or othersuitable material for the processing environment being encountered.Similarly, each profile thermocouple array 180 is preferably sealedwithin a quartz thermocouple tube 178 along the entire length exposed tothe process chamber 16. It is alternatively possible to use fittings 174to mount other attachments or accessories in addition to the common onesexplained above.

Because of the high temperatures encountered, it is desirable to includea means for cooling where the fittings 174 receive the accessoriesmounted therein. This is desirable in order to cool the seals used aboutthe fitting and prevent premature failure of the seals or othercomponents of the accessory being mounted. FIG. 10A shows in detail, anO-ring seal 182 which is placed around each fitting 174 at a location soit becomes trapped between the base piece 164 and the support 162 whenassembled together. As shown in FIG. 10A, a port 184 is formed in thebase throat piece 164 in order to allow placement of the thermocouplearray 180 (or delivery tube 176 not shown in FIG. 10A) therethrough andinto the process chamber 18. Likewise, a support port 190 is formed inthe base support 162 through which the end of fitting 174 are similarlyreceived as illustrated in FIGS. 10A and 11. In this construction,0-ring 182 serves to form a circumferential seal between the base throatpiece, base support piece and fitting which seals the fluid coolingcavity 170 from ports 184 and 190.

The ports 190 have recessed regions 191 along the upper surface of piece162 as shown in FIGS. 10A and 11. The recessed regions allow a coolingfeature to be installed adjacent to each 0-ring 182. The preferredcooling feature is in the form of a cooling air distribution disk 196.

FIGS. 16-18 show details of the cooling feature in enlarged detail. AsFIG. 17 shows, each port 190 is provided with the adjacent recessedregion 191 which forms a seat. Disk 196 is mounted in the recessedregion 191 and is secured thereto using fasteners 193 (FIG. 17) whichextend through apertures 194 formed through the disk 196 and into basesupport piece 162 at each port. Disk 196 also has a central aperture 201through which the thermocouple array 180 or gas supply tube 176 extendup and into the processing chamber.

A cooling supply port 198 extends through base support 162 to providefluid communication of cooling air, nitrogen or other fluid to therecessed area 191 for distribution within an annular distribution cavity216. Cavity 216 is in fluid communication with exhaust ports 199 whichsupply cooling fluid to the space adjacent to O-ring 182. Supply ports198 can be threaded to facilitate connection of supply lines (not shown)thereto. FIG. 17 also shows that disk 196 has a beveled O-ring seat 200that acts to position and compressively seat the O-ring seal 182 betweenthe base plate 162, disk 196, and accessory 176 or 180.

FIGS. 10 and 10A also show a base cooling cavity 170 between the basepiece 164 and the base support member 162. FIG. 10 shows that cavity 170is further defined by an exit duct 251 which is connected securelywithin the central aperture of base support member 162. The exit duct251 is provided with a flange 252 which is used to mount an exit ductend piece 253 using fasteners 254. The exit duct 251, exit duct endpiece 253, base piece 164, and base support member 162 enclose the basecooling cavity 170. A seal 261 (FIG. 10A) seals between the members 162and 164 at the outer perimeter of the base cooling cavity 170. A seal269 (FIG. 10) seals between the parts 251 and 253.

The exit duct end piece 253 is provided with one or more cooling gasports 262 which supply nitrogen, air or other suitable cooling fluid tothe base cooling cavity 170. As shown the cooling gas ports 262 areincludes at plural locations about the circumference and cooling fluidis distributed to each port within an annular distribution channel 263covered by a cover 264. Cooling fluid supplied through ports 262 ispassed through cavity 170 and exits through a number of exhaust holes263 (see FIG. 12) formed in the base support member 162.

The exit duct end piece 253 also has a cooling channel 255 similar tothe cooling channels 222 described above. Cooling channel 255 includes acooling channel cover 256. Cooling water or other suitable fluid ispassed about the circumferential cooling channel to cool the exit ductend piece 253.

The exit duct end piece 253 is also advantageously provided with a exitduct bottom flange 257. The exit duct bottom flange 257 mounts aplurality of J-hook fasteners 258 which are used to mount piping, ormore preferably the outflow cooler 600 described below. The piping orcooler are sealed against the bottom end surface of the base member 164using an outflow main seal 259. The outflow is also preferably providedwith an outflow seal heat shield 607 (FIG. 10) which reduces heat to theseal and allows the cooling jets 262 to maintain lower temperatures forseal 259. The heat shield 607 has a support lip which is advantageouslysupported upon a ledge formed along the inner diameter of the base piece164.

Pedestal Assembly

FIGS. 3, 4 and 10 also show that the thermal processor 10 is preferablyprovided with a pedestal assembly 163. Pedestal assembly 163 includes apedestal collar 271 which rests upon the quartz base throat piece 164.Collar 271 is provided with accessory apertures 272 (FIG. 10A) as neededto allow extension from fittings 174 up into the processing chamber. Thecollar preferably rests partially within a recessed area defined byshoulder 273 (FIG. 10A) along the upper face of base throat piece 164 tohelp maintain proper positioning of the collar thereon.

The pedestal collar 271 supports a pedestal cylinder 281 which isaffixed sets upon a recessed end area of the collar. The pedestalcylinder extends upwardly and supports a pedestal headpiece 283.Headpiece 283 preferably has a plurality of pedestal holes 284 whichallow gases which are exhausting from the processing chamber to passtherethrough. The upper end surface of the headpiece is advantageouslyprovided with locating features for maintaining the proper position ofthe processing boat 12 thereon. As shown, the locating features includea pair of locating projections 336. The end surface can also include acentral recessed area 286 which further serves as a locating feature.The central recessed area 286 can alternatively be an aperture extendingthrough the end surface to further facilitate circulation of gaseswithin the pedestal.

The pedestal collar 271 is preferably made of opaque quartz as is thepedestal cylinder 281. The pedestal headpiece is preferably made fromsilicon carbide. Both are formed using well-known production techniquesfor these materials.

The pedestal assembly can also advantageously be provided with anoptional pedestal heater (not shown) which includes an electricresistance heating element. Although not preferred, the pedestal heatercan be used in some processing situations where heat input from below isdesirable.

Fluid Cooling Circuits

The thermal processor 10 is preferably provided with two main fluidcooling circuits. The first or inner fluid cooling circuit passesbetween the outer surface of the processing tube 18 and the innersurface of the furnace liner 82. The first cooling circuit has a firstflow path 75. The second or outer fluid cooling circuit passes along theoutside of the furnace liner 82 and along the inside surfaces of theheating enclosure subassembly 88. The second cooling circuit has asecond flow path 77. The first and second fluid cooling circuitspreferably extend in opposite or counterflowing relationship to providemore even temperatures during cooling. Air is preferably utilized as thecooling fluid in both circuits. Alternatively, various other thermallyconductive gases can be utilized.

FIG. 10 shows that the first cooling circuit flow is preferablyintroduced through the cooling fluid supplies 99, passageways 89 and isdistributed via annular chamber 46. The cooling flow passes throughports 45 an into the space between liner 82 and processing tube 18. FIG.3 shows that the flow moves upwardly to the top of the liner and isexhausted via connection fitting 85. The first fluid cooling circuitthen continues through the conduit 122. Conduit 122 includes a flange341 which is engaged by a spring-loaded gasket 342 that seals about theconduit. The upper end of conduit 122 extends through an aperture intoand flow plenum 349. Flow plenum 349 also is connected to receive theflow from risers 139. The area about conduit 122 and between plenum 349is advantageously packed with a suitable high temperature packing 347,such as a fibered ceramic wool material.

Flow plenum 349 also supports and serves as an intake plenum for a flowmover 350. Flow mover 350 is preferably an air flow amplifier operatingon the coanda effect and driven with compressed air. The unit functionsas both a first fluid flow mover for the first fluid cooling circuit,and a second fluid flow mover for the second cooling circuit. Oneappropriate flow mover is manufactured by Exair Corporation. Other typesof flow movers or motors are possible, although the preferred flow moveris advantageous in that no moving parts are needed and thus the risk ofparticles being generated is reduced.

The cooling fluid mover 350 has an outlet 351 which is movablevertically with the head assembly 25. Thus it is advantageous to have aflexible duct 359 which expands and contracts in length to accommodatethis movement. Flexible duct 359 is preferably a spiral spring memberwhich can extend and contract as needed to accommodate the verticalmotion.

The second fluid cooling circuit has a flow 77 which is preferablyintroduced through exterior ports 120 near the top end of the heatingenclosure subassembly. The second coolant flow 77 is distributed withinannular manifold chamber 118 so as to be evenly introduced through theindividual ports 110 into the space between the heating enclosuresubassembly and the furnace liner. The flow then preferably movesdownward and is passed out through heater base 102 via passageways 111.Passageways 111 are in fluid communication with the annular chamber 126which accepts the flow from the numerous passageways. The second coolingflow then passes out through side ports 124. The flow from side ports124 are preferably taken via riser ducts 139 to the flow plenum 349 andflow mover 350.

Process Chamber Outflow

The thermal processor 10 also includes a process chamber outflow whichis designed to reduce temperatures in the associated parts of theprocessor. As FIG. 4 illustrates, the outflow preferably includes anoutflow baffle array 278. The outflow baffle array is shown in greaterdetail in FIG. 21. The preferred construction includes a first or topbaffle 501. Top baffle 501 deflects the downwardly exiting process gasesoutwardly and causes the gases to pass about the outer periphery of thetop baffle.

The baffle array also includes a second or intermediate baffle 503.Second baffle 503 extends outwardly to the inner wall of the processtube 18 to deflect the flowing gases inwardly and through a centralaperture 504. The top baffle is supported upon the second baffle usingspacers 505. Spacers 505 are preferably bonded to the second bafflealthough other constructions are alternatively possible.

The baffle array also includes a third or bottom baffle 508 which hasseveral peripheral openings or notches 509 which allow the exiting flowof processing gas to move therethrough. The third baffle's central areais solid to force the flow through peripheral openings 509. Theperipheral spokes or lugs 510 support the array upon a suitable supportsuch as an inner liner 520. The baffle array reduces the likelihood thatgases or other contaminants contained in the outflow chamber below maymigrate upwardly and into processing chamber 16.

FIG. 20 shows the inner liner 520 in isolation from other parts of theprocessing chamber outflow components. The inner liner 520 is supportedupon a ledge formed upon the pedestal collar 271. To accomplish this,the inner liner includes a top peripheral flange 521.

The inner liner 520 has an entrance or mouth 522 at a top end and anexit or discharge 527 at a bottom end. The inner liner 520 is preferablyformed as a sleeve which has an upper portion 523 and a lower portion524. The upper portion is frusto-conically shaped. The convergingdownwardly conical shape directs the outflowing gases into the lowerportion 524. The lower portion forms a downward extension which canadvantageously be formed in a cylindrical shape. The inner liner shieldsthe lower portions of the base plate assembly from direct impingementfrom the outflowing hot processing gases and thereby reducestemperatures of such parts. The inner liner is advantageously made fromquartz or other suitable materials for the processing gases being used.

Processing Chamber Outflow Cooler

FIG. 4 shows that it is also possible to include an outflow cooler 600which extends the outflow section of the thermal processor and reducesthe temperature of outflowing exhaust gases from the upstream processingchamber. Outflow cooler 600 is downstream from other portions of theoutflow explained above. The outflow cooler preferably includes anoutflow cooler sleeve or casing 602. Casing 602 preferably is made froma relatively strong and thermally conductive material, such as stainlesssteel.

The casing can advantageously be provided with a casing top flange 604.Top flange 604 allows the cooler 600 to be at least partially supportedupon the exit duct end piece 253 utilizing the J-hook fasteners 258coupled with flange 257.

The bottom of casing 602 is advantageously provided with a dischargeport 609. The discharge port is adjacent to a casing bottom shoulder608.

The outflow cooler 600 also preferably includes an outflow cooler lining605. Lining 605 is preferably made from a material which is non-reactiveto the processing environment. A preferred material is Teflon™ polymermaterial. The Lining 605 is advantageously provided with a coupling heador flange 606. The upper end face of coupling head or flange 606 engageswith the main outflow seal 259 to form a fluid tight coupling andcontinuation of the outflow side walls. The bottom portions of thelining 605 include a shoulder 640 which bears upon the shoulder 608provided in the casing. The lining also has a discharge port wallsection 643. Both shoulder 640 and discharge section 643 are formed witha heavier wall thickness than the side walls to help withstand the hightemperatures and load imposed by carrying the flow diverter thereon.

The outflow cooler 600 also includes a heat exchanger 621 for removingheat from the side walls of the outflow cooler casing. The heatexchanger can be mounted upon the casing or be formed as part of thesidewalls of the casing. As shown, casing 602 is provided with a helicalcooling tube array which spirals along the outside surface of thecasing. The cooling tube array is mounted in a manner which providesgood thermal conductive coupling with the casing. This can be done by avariety of techniques including simple contact or physically couplingusing welding or brazing. Alternatively, the casing could be constructedwith double walls and the coolant be trained therethrough to removeheat.

The outflow cooler 600 also preferably includes a flow diverter 630.Flow diverter 630 is centrally mounted to divert the flow of outgoinggases against the cooled side walls of the cooler. The flow diverter isadvantageously made from a temperature resistant material, such asquartz, to withstand the direct flow of hot processing gases. Because ofthe reduced cross-sectional area, the flow diverter increases thevelocity of the outflowing gases along the cooled interior side wallsprovided by liner 605. The diverter also brings all outflowing gasesinto closer proximity with the cooled side walls. This improves heatexchange and reduces the temperature of the outflowing gases.

The flow diverter 630 is advantageously formed as an annular body havingrelatively thin shell which can easily respond to temperaturevariations. The top end 631 of the flow diverter is preferably providedwith a bulbous shape which improves flow thereover. The bottom end wall632 has a vent hole 635 which allows gases to move into or from theinterior of the flow diverter as temperatures vary.

The flow diverter 630 is also preferably provided with a set of flowdiverter feet 636. Feet 636 are preferably provided in a tripodarrangement. The feet can be bonded to the bottom end wall 632. Feet 636are advantageously made of quartz or otherwise made of the same materialas the flow diverter. In one preferred form of the invention, the feet636 have sloped bottom feet surfaces which set in complementaryrelationship with a sloped shoulder 640 formed on the liner 605.

FIG. 31 further shows a preferred outflow plumbing arrangement used withthe processor 10 when the outflow cooler 600 is utilized. The outflowfrom cooler 600 at discharge 609 is plumbed to a tee 651. Tee 651branches to a gas discharge line 653 which has an elevated section 654which is above the tee 651. A control valve 658 is controlled by a valvecontroller 659 which is controlled directly or indirectly by the generalcontroller described below. A purge fitting 660 is applied upstream ofthe control valve 658 to purge the outflow piping with nitrogen or othersuitable purge gas. The purge fitting 660 is supplied with purge gas ascontrolled by purge flow control valve 665. Valve 658 controls flowthrough the gas discharge branch 653. In one preferred form, the valves658 and 665 can be integrated, to provide simultaneous control of bothfunctions from a single unit. The downstream side of control valve 658is connected to a facilities exhaust at an elevation below tee 651.

FIG. 31 also shows a liquids discharge branch 680 which extendsdownwardly from tee 651. The liquids discharge is provided with a waterflush via flush connector 681 which is provided with a stream ofdeionized water controlled by flush control valve 683. A flow indicator684 can advantageously be employed. The liquids outflow from connector681 is passed through a gas trap 687 and then to a suitable drain fordisposal of acid containing waste streams.

Methods and Operation

The thermal processor 10 is preferably operated using the followingmethods. Wafers 14 or other semiconductor articles are first processedby loading the articles into the processor. This is advantageously doneby opening the access door 9 and either manually or automaticallyplacing the articles into the loading chamber 11. After the wafers havebeen placed into the loading chamber, then the wafers are held byinventorying the wafers on inventory stand 13 or other suitablestructure.

In processor 10 the inventoried wafers are then preferably relocatedfrom the inventory position by transferring the wafers. This is done bymoving the wafers. The moving operation typically involves removing thewafers from the wafer carriers 17 using the wafer transfer mechanism 48.Each wafer is moved by relocating the wafer from the carrier into asuitable location adjacent to the loading chamber. In the most preferredmethods the relocating takes place by moving the wafers from theinventory positions to the pre-load boat 54. The relocating preferablytakes place by moving the wafers at the same or nearly the sameelevation so that vertical changes are avoided.

Processing also preferably includes the step of opening the processingvessel to allow access to chamber 16. This is done by retracting thehead assembly 25 upwardly. The retracting is capable of being done inseparate steps. A first retracting step includes retracting the furnaceheater assembly 22 upwardly using actuators 28. This retracting caneither be followed or concomitantly associated with retracting theprocessing tube assembly. The processing tube assembly is liftedupwardly in the retracting step using processing tube lift actuators 26which are retracted.

Processing using thermal processor 10 also preferably includes loadingthe wafers or other semiconductor articles 14 into the processing boat12. This performs by providing an array of semiconductor articlessupported upon the processing boat. The loading is advantageouslyaccomplished by transferring the wafers from the pre-load array 54 tothe processing boat array using wafer transfer 48. This transferring andrelocating preferably takes place by moving the wafers at the same ornearly the same elevation so that vertical changes are avoided.

The methods and operation further typically involve closing theprocessing vessel to substantially enclose the processing chambertherewithin. The closing operation advantageously includes extending theprocessing tube 18 downwardly and over the processing array. This ismost preferably accomplished by extending the actuators 26 and loweringthe lift ring 30. The closing operation can also involve extending theprocessing head 25 downwardly. This is advantageously done by extendingthe actuators 28 and moving the furnace heater assembly 22 downwardly.If the processing tube assembly is already lowered, then the actuators26 are simultaneously retracted as the actuators 28 are extended.

The methods also include providing a furnace heater having a furnacechamber within which the processing vessel is positioned. The methodsalso include heating the processing vessel and processing chamber withthe furnace heater assembly 22. The heating can be done alone or withother processing steps involving exposing the semiconductor articles tovarious chemicals, particularly gases, as is well-known in the art.During processing, the processing chamber can be supplied with desiredprocessing gases via tube 176. The outflowing gases are then cooled bydischarging them through the preferred cooler 600.

After the heating is accomplished then the articles are cooled. Thecooling step is preferably effected by providing or flowing a firstcooling fluid flow adjacent the processing vessel. The first coolingfluid flow is advantageously accomplished by flowing the cooling fluidnear the processing chamber seal and then upwardly along the outside ofthe processing tube 18.

The cooling step is also preferably effected by providing or flowing asecond cooling fluid flow adjacent to the furnace heating assembly. Thesecond cooling fluid flow is advantageously accomplished by flowing thecooling fluid downwardly and along the inside of the heater subassembly.The second cooling fluid flow is preferably done in countervailingrelationship to the first cooling fluid flow. The countervailingrelationship is best done segregated along opposite sides of a commonthermally conductive baffle, such as the furnace liner 82.

The methods also preferably include opening the processing chamber aftercooling a desired amount of time. The opening is the same or similar tothat described above.

The methods further preferably include unloading the wafer boat 12, suchas by using the automated wafer transfer 48. The unloading of theprocessing boat is advantageously done by transferring the wafers orother semiconductor articles to the cooling boat 56. Thereafter thewafers can continue to cool in the cooling boat.

The methods can further include transferring the articles 14 from thecooling boat to the inventory stand 13, and then inventorying thearticles thereon until removed. The transferring is advantageously doneby moving the articles to wafer carriers 17 or similar carriers forholding the articles.

Furnace Power Controller

It will be appreciated that it becomes necessary to use a sophisticateddynamic control system in order to achieve a uniformed thermaldistribution within a processing chamber 16 during various processingcycles. Temperature must be dynamically monitored outside the processingchamber via spike thermocouples 128 and 130 as well as within theprocessing chamber via profile thermocouples 180. At the same time,timely and accurate decisions must be made on when and how long eachheater element segment 90-96 and 101 should be activated and deactivatedin order to achieve the desired uniform thermal processing environmentin the process chamber 16. To achieve this result, a furnace powercontroller 350 is used. The furnace power controller 350 is preferablyimplemented in conjunction with a model based controller 352 in order todynamically and accurately control the furnace heater elementsresponsively to a desired thermal model configured on controller 352 andmeasured temperatures obtained via the thermocouples.

The furnace power controller 50 is hosted on a control computer, such asan Intel based 80486 DX model controller or other suitable controllers.Likewise, the preferred model-base controller is preferably hosted on aseparate computer of the same or similar design. The model basedcontroller implements a real-time control system that employsmulti-variable real-time feedback control. Preferably, the model-basedcontroller 52 is a software-based system which uses empirically derivedparameters which provide relatively good predictive estimation of wafertemperatures. One possible system is described in U.S. Pat. No.5,517,594. Another is described in U.S. patent application Ser. No.08/791,024, filed Jan. 27, 1997, entitled "Model Based TemperatureController for Semiconductor Thermal Processors". Both such examplesystems are incorporated by reference.

Controller 352 forms a high fidelity dynamic model that describes thebehavior of wafer temperatures and key film and device properties suchas oxide and polysilicon film thickness and diffusion drive-in that areneeded to optimize wafer uniformity and processing cycle time. Thecontroller 352 consists of optimization software comprising a model ofthe furnace that accurately describes the thermal behavior of aparticular furnace resulting from data acquired from test experimentsthat enable characterization of the heater power requirements andthermocouple measurements.

The resulting control system 348 illustrated in FIG. 23 can implementcomplex multi-variable controllers to regulate application of heat viathe heater elements which represents a significant enhancement overexisting prior art commercial PID controllers. Preferably, the furnacepower controller 350 and the model-base controller 352 both utilize astandard rack mount that fits directly into computer control cabinet 58forming part of the tail section 42. In operation, the furnace 22 iselectrically coupled to send thermocouple measurements as input to themodel-base controller 352 as shown in FIG. 23. Controller 352 receivesthe thermocouple signals and sends heater command signals directly tothe furnace. Concurrently, the model-base controller 352 sends statussignals to the furnace power controller 350 and the controller 350 sendsset point signals to the controller 352.

Controller 352 is preferably a multi-variable controller having twotypes of set point trajectories; namely, a multi-variable control havingflat trajectories and a dynamic optimization with time-bearing set pointtrajectories. In this manner, a model-based temperature is characterizedin order to make wafer temperatures follow the desired set pointtrajectories from the two above mentioned trajectory types. In thismanner, a model-based temperature control for controller 352 employs amulti-variable controller which uses an on-line model to generateestimates of wafer temperatures.

FIG. 24 is a block diagram of the power controller circuit 354comprising a preferred form of furnace controller 350. Circuit 354 formsa module that controls the actual power supply to each of the heatingelements 90-96, 101 and any ancillary pedestal heater which might beoptionally included in the furnace. Preferably, silicon controlledrectifiers (SCR) 392 are implemented to control the actual power supplyusing the phase angle firing characteristics of the SCR's. FIG. 24depicts the circuit of a single power control module capable ofsupplying power to two heater zones in the furnace, with independentcontrol available to supply power to each of the two zones. For example,heater elements 90 and 91 can be supplied by a single module as depictedin FIG. 23. Additionally, the two zones supplied by a single modulepreferably will be connected to the same phase of an alternating currentpower line.

As shown in FIG. 23, a microprocessor based host computer 356 supplies aset point command to the power control module 354 by way of a serialcommunications link 358. A communication interface 360 on module 354relays the set point command to a dedicated microprocessor 362 on themodule. The set point command received by the microprocessor 362 definesthe desired load power in watts. In this manner, host computer 356 isconfigured to read the measured load power in watts over the serialcommunication link 358. Hence, a gang of power controllers may share thesame serial communications link 358, wherein each controller module orcircuit 354 is assigned a uniquely identifiable address.

A circuit module 354 constructed according to the layout of FIG. 24provides several unique features. In one case, the host computer 356comprises the microprocessor of the model-base controller 352 such thatthe input from the host computer that controls the two heater elementsconnected to the module is the desired load power and the watts obtainedfrom the model-based controller. A second desirable feature resultsbecause circuit module 354 measures both the load voltage and the loadcurrent for each element such that the actual power delivered to eachload, or element can be calculated. An additional unique feature resultsbecause circuit module 354 forms a true power controller. Moreparticularly, circuitry in the module adjusts the firing angle of SCR'svia a control loop in order to achieve the desired power from themodel-based controller 352 delivered to the load in the presence ofvariations in line voltage and load impedance. Furthermore, in responseto a command via communication link 358, the circuit module 354 willreport the measured power presently being delivered to the load, inwatts. Another unique feature results since the power measurementcircuitry in the module determines the load power on a cycle by cyclebasis which enables the circuit module to respond rapidly to changes inline voltage or load impedance.

A pair of power measurement circuits 366 and 367 and a pair of SCRtrigger timing circuits 368 and 370 are configured independently of thefrequency of the alternating current power line. Therefore, noadjustments to the circuits are needed when operating at 50 or 60 hertz.

In order to better understand the functional characteristics of circuitmodule 354, various circuit subassemblies are further depicted in FIGS.25-29. As shown in FIG. 24, circuit 354 includes a power switch circuitconfigured to enable the switch to conduct both during the positive andnegative half cycles of an alternating current wave form provided in theline power. A separate power switch circuit 372 and 374 is provided foreach heater element. The trigger timing circuits 368 and 370 are shownconfigured to each form a timing circuit, respectively wherein a PLLclock generator circuit 380 generates a high frequency clock from thealternating current (AC) power line to synchronize operation of eachtrigger circuit.

A power measurement circuit 366 and 367 is shown configured to measurethe actual power delivered to the load from each heating element on acycle by cycle basis. Each power measurement circuit 366 and 367 isshown configured to an A/D converter 386 and 388 that produces a digitaloutput consisting of an integral of the input voltage over a completecycle of the AC line voltage. Each A/D converter includes a synchronousvoltage to frequency (V-F) converter 390 and 392, respectively, thatproduces a train of output pulses representing a discrete amount ofcharge delivered into the analog input. The pulses are accumulatedduring each cycle and counted wherein the microprocessor reads thestored value in a latch resulting from the count such that the averagecharge delivered to the input of the converter can be determined bycounting the pulses in the counter at the end of the cycle which will beindependent of the frequency of the AC line.

In the above manner, the average power delivered to the load, orparticular heater element, during one cycle can be determined from thenumber of pulses in the counter at the end of a cycle. Hence, in thismanner, the furnace power controller 350 can deliver set point commandsto the model-based controller 352 over a serial communications link. Theset point commands are the actual load power transmitted to each heatingelement which is received by controller 352 in order to evaluatedynamically new heater commands.

With particular reference to FIG. 25, each power switch circuit 372 isformed from a pair of semiconductor controlled rectifiers (SCR's) 392shown connected back to back and parallel with a metal oxide varistor(MOV) 394 and a resistor/capacitor (RC) snubber 396. The SCR's, varistorand snubber are interconnected in parallel with diode steering logiccircuitry 398 formed by a portion of the trigger circuit 368 and 370discussed hereafter. The steering diodes in the circuitry 398 route atrigger pulse to one of the SCR's that is forward biased at that time.As a result, the power switch is enabled to conduct during both halfcycles of an AC line power. Additionally, both SCR's are protected fromdamage by over voltage transients through electrical configuration ofthe MOV 394 and snubber 396. In the case of an over voltage transient,varistor 394 and snubber 396 cooperate to shunt or limit the rate ofrate of rise of voltage where the peak of voltage across the SCRdevices, especially when switching from a conductor to a blocking stateor when subjected to an external voltage transient. Therefore, the rateof rise or fall of current through the device when switching on or off,respectively is limited.

FIG. 26 depicts trigger circuit 374. Trigger circuit 368 is similarlyconfigured. As shown, the trigger circuit consists of a data latch 369,a counter 371, an optical isolator 373 and a firing circuit 375. Thedata latch is configured to hold a digital value written to it by themicroprocessor 362. The value stored in the data latch controls the faceangle at which the SCR's 392 will be triggered. The counter counts thepulses of the high frequency clock generated by the PLL clock generatorcircuit 380 discussed hereafter. When a zero crossing pulse occurs, thecounter is preset to the value stored in the data latch. The counterthen counts up from this preset value until it reaches a maximum count,at which time a flip-flop 377 is set. The flip-flop provides a signal tothe optical isolator 373. The optical isolator in response to the signaldrives the firing circuit which amplifies the output signal from theoptical isolator to a pulse of sufficient amplitude to trigger the mainSCR's. Additionally, steering diodes 379 are provided in the firingcircuit in order to route the trigger pulse to which ever SCR is forwardbiased at that time.

For the case where the counter is preset with a value near it's maximumcount, the counter will count up to it's maximum count with few inputclocks. As a result, the power switch will be triggered early in an ACcycle, thereby causing it to conduct for most of the current half cycleof the AC power. As a result, a large amount of power will be deliveredto the load. In the event the counter is preset with a value of nearzero, it will take many input clocks to count up to it's maximum count.In this event, the power switch will be triggered near the end of thecurrent half cycle of the AC line power, thereby resulting a littlepower delivered to the load. As a general rule, the number of clockpulses produced by the PLL clock generator circuit 380 during each halfcycle is found to be equal to the maximum count of the counter.

The phase lock loop (PLL) clock generator circuit 380 generates a highfrequency clock that is synchronized at the phase of a transmittedsignal; namely, an AC power line signal. The synchronized high frequencyclock is used by both A/D converters 386 and 388 as well as the SCRtrigger circuits 368 and 370. As shown in FIG. 26, the clock generatorconsists of a phase locked loop circuit 400 interconnected with adigital counter 402 and gating circuits 404.

In operation, the digital counter 402 is driven by a high frequencyvoltage controlled oscillator (VCO) 406. In operation, the phase lockedloop circuit 400 adjusts the frequency of the oscillator 406 until theoutput pulses from the counter in synchronization with the input pulsesin the zero cross detector at input line 408. As a result, theoscillator 406 becomes synchronized to the AC line voltage, and theresulting frequency of the oscillator becomes a multiple of the AC linefrequency. The high frequency oscillator 406 is coupled to the gatinglogic circuits 404 which is configured to supply the above resultingclock signal to the A/D converter 386 and 388 and the trigger circuits368 and 370. The gating circuit 404 is configured to supplysynchronizing signals to both the A/D converter and the trigger circuitthrough one of several commonly known circuit implementations.

Referring now to FIG. 27, the power measurement circuit 366 isillustrated utilizing a step down transformer 410, a current transformer412 and an analog multiplier 414. Circuit 367 is similarly constructed.The power measurement circuit is configured to measure the actual powerdelivered to the load, e.g. a heater element, on a cycle by cycle basis.The microprocessor 362 uses the delivered power information in order toadjust the conduction angle of the SCR's 392 in order to maintain thedesired power output in the presence of variations in line voltage andload impedance.

Circuits 366 and 367 are each configured to compute a value for loadpower from measurements of load voltage and load current. Aninstantaneous load voltage value is reduced to a suitable value by wayof the step down transformer 410. Additionally, transformer 410 alsoisolates the circuit from the power line. The output voltage from thestep down transformer is shown applied to an input of the analogmultiplier 414. Similarly, the load current from a heating element 90 issampled with the current transformer 412. An output voltage from thecurrent transformer 412 is amplified to a suitable level afterwhich itis applied to the second input of analog multiplier 414. Multiplier 414receives a pair of output voltages to produce a voltage output alongline 418 that is proportional to the product of the load voltage andload current and is essentially the instantaneously load power. Hence,line 418 applies the instantaneous load power as an input to the A/Dconverter 386, 388. Additionally, a power switch 416 is seriallyconnected with respect to the power line.

FIG. 28 depicts a preferred construction for the A/D converter 386 and388 which forms an integrating charge balance converter. The converteris configured to provide a digital output that comprises the integral ofthe output voltage over a complete cycle to the AC line voltage. Moreparticularly, an analog input 420 is fed into the synchronous voltage tofrequency (V-F) converter 390, such that the converter 390 produces atrain of output pulses with each output pulse representing a discreteamount of charge into the analog input. The pulses are fed into acounter 422 that accumulates the number of pulses during a completecycle. At the end of each cycle, the count in the counter is stored in alatch 424 and the counter is reset for the next cycle. Microprocessor362 then reads the value stored in each latch wherein:

The charge represented by each pulse from the V-F is

    q=it,

where i is a constant current and t is the period of the clock to thecircuit

The total charge delivered to the input during one cycle of the AC linevoltage is then represented by the number of pulses in the counter atthe end of the cycle.

    q.sub.tot =Nit,

where N is the number of pulses in the counter.

The average charge delivered during the cycle will be the total chargedivided by the length of the cycle. ##EQU1## where T is the length ofone cycle of the ac line. But the PLL causes the frequency of the clockto be a fixed multiple of the AC line frequency,

    T=mt,

thus, ##EQU2## where m is the ratio of clock frequency to linefrequency.

The resulting average charge delivered to the input of the V-F convertercan then be determined from the number of pulses in the counter at theend of the cycle and is independent of the frequency of the AC line.

Because the voltage applied to the input of the V-F converter isproportional to the instantaneous power and load, the average chargeover a cycle will be proportional to the average power and the load overthe cycle. Therefore, the average power delivered to the load during onecycle can be determined form the number of pulses in a counter at theend of the cycle.

General Controller

In addition to the power control system described above, there is also ageneral system controller 800 which can advantageously be provided inthe form of one or more preferably plural microprocessor based systems,such as the 80486 DX systems described above or equivalents thereto. Thegeneral controllers connected to various components and sub-controllersused to provide proper operation of the thermal processor. FIG. 30 showsconnection with the touch screen display--input 15d, operator switches15a and 15b, and front panel indicator lights 15c and 15e. Generalcontroller 800 is also connected to the furnace power controller 350.Furnace power controller 350 preferably has plural control functionswhich are dedicated to the plural heating zones used in the processor10. Power controller 350 receives signals from the general controller800 used in control of the processor and also receives model basedcontrol signals from model based controller 352 and associated thermalsensor information from sensors 128 and 180. The model based controlleris also connected to receive and provide control signals to controller800. Thermal sensors 180 and 128 provide temperature information whichis primarily used in the power controller but which is also supplied tothe general controller for use in data display and other controlfunctions.

General controller 800 also controls the actuators 26 and 28 which poweroperation of the head assembly 25. A variety of fluid valves areschematically shown as processing fluids control valves 803. The generalcontroller also provides and receives signals to and from a wafertransfer sub-controller 804 associated with the wafer transfer 48 whichcontrols the function of the wafer transfer.

Controller or controllers 800 also preferably take advantage of shareddata memory 806 which can be utilized to the advantage of the generalcontroller or other controllers forming part of the control system.

Manner of Making

The thermal processor 10 is made using the preferred materials indicatedabove or alternative materials which can perform under the conditionsindicated. The various components and features described are provided byusing know metal working and other machining techniques to provide thedescribed structures and explained operation. A variety of manufacturingtechniques can alternatively be used to make the preferred embodimentshown herein or other thermal processors according to the invention.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A thermal processor for treating a plurality ofsemiconductor articles, comprising:a framework; a furnace heater mountedupon the framework and having a furnace chamber therewithin; aprocessing vessel having a processing chamber for treating thesemiconductor articles, said processing chamber having an outflow with adischarge opening through which heated exhaust gases are discharged; anoutflow cooler connected to receive exhaust gases from the dischargeopening, said outflow cooler having a heat exchanger which removes heatfrom the outflow cooler by passing a fluid coolant therethrough; a flowdiverter positioned within the outflow cooler to direct the flow ofexhaust gases against walls of the outflow cooler.
 2. The thermalprocessor of claim 1 wherein said flow diverter directs exhaust gasesagainst sidewalls of the outflow cooler.
 3. The thermal processor ofclaim 1 wherein the heat exchanger is arranged to remove heat from saidwalls of the outflow cooler.
 4. The thermal processor of claim 1 whereinsaid flow diverter is an annular flow diverter coaxially positionedwithin the outflow cooler to direct the flow of exhaust gases againstsidewalls of the outflow cooler.
 5. The thermal processor of claim 1wherein said flow diverter is an annular flow diverter coaxiallypositioned within the outflow cooler to direct the flow of exhaust gasesagainst sidewalls of the outflow cooler, and wherein the heat exchangeris arranged to remove heat from said sidewalls.
 6. The thermal processorof claim 1 wherein said outflow cooler further includes:a casing towhich the heat exchanger is mounted to remove heat therefrom; a linermounted within the casing in contact therewith to transfer heat throughthe liner into the casing and to the heat exchanger.
 7. The thermalprocessor of claim 1 wherein said outflow cooler further includes:acasing to which the heat exchanger is mounted to remove heat therefrom;a liner mounted within the casing in contact therewith to transfer heatthrough the liner into the casing and to the heat exchanger; and whereinthe flow diverter is positioned within the outflow cooler to direct theflow of exhaust gases against sidewalls of the outflow cooler.
 8. Thethermal processor of claim 1 wherein said outflow cooler furtherincludes:a casing to which the heat exchanger is mounted to remove heattherefrom; a liner mounted within the casing in contact therewith totransfer heat through the liner into the casing and to the heatexchanger; and wherein the flow diverter is annular and coaxiallypositioned within the outflow cooler to direct the flow of exhaust gasesagainst sidewalls of the outflow cooler, and wherein the heat exchangeris arranged to remove heat from said sidewalls.
 9. The thermal processorof claim 1 wherein the flow diverter is an annular member.
 10. Thethermal processor of claim 1 wherein the flow diverter has a thin shell.11. The thermal processor of claim 1 wherein the flow diverter has athin shell and a vent which allows gases to move into or from theinterior of the flow diverter.
 12. The thermal processor of claim 1wherein the flow diverter has a thin shell and a vent which allows gasesto move into or from the interior of the flow diverter, said flowdiverter resting on feet to support the diverter away from walls of theoutflow cooler.
 13. The thermal processor of claim 1 wherein the flowdiverter has a thin shell and a vent which allows gases to move into orfrom the interior of the flow diverter, the vent being along adownstream surface of the flow diverter.
 14. The thermal processor ofclaim 1 wherein the flow diverter has an upstream end which is bulbousin shape toward the flow of exhaust gases.
 15. A thermal processor fortreating a plurality of semiconductor articles, comprising:a framework;a furnace heater mounted upon the framework and having a furnace chambertherewithin; a processing vessel having a processing chamber fortreating the semiconductor articles, said processing chamber having anoutflow with a discharge opening through which heated exhaust gases aredischarged; an outflow cooler connected to receive exhaust gases fromthe discharge opening, said outflow cooler having:a heat exchanger whichremoves heat from the outflow cooler by passing a fluid coolanttherethrough; a casing to which the heat exchanger is mounted to removeheat therefrom; a liner mounted within the casing in contact therewithto transfer heat through the liner into the casing and to the heatexchanger; a flow diverter positioned within the outflow cooler todirect the flow of exhaust gases against sidewalls of the outflowcooler, and wherein the heat exchanger is arranged to remove heat fromsaid sidewalls.
 16. The thermal processor of claim 15 wherein the flowdiverter is positioned in an approximately coaxial relationship with thesidewalls.
 17. The thermal processor of claim 15 wherein the flowdiverter is an annular member.
 18. The thermal processor of claim 15wherein the flow diverter has a thin shell.
 19. The thermal processor ofclaim 15 wherein the flow diverter has a thin shell and a vent whichallows gases to move into or from the interior of the flow diverter. 20.The thermal processor of claim 15 wherein the flow diverter has a thinshell and a vent which allows gases to move into or from the interior ofthe flow diverter, said flow diverter resting on feet to support thediverter away from walls of the outflow cooler.
 21. The thermalprocessor of claim 15 wherein the flow diverter has a thin shell and avent which allows gases to move into or from the interior of the flowdiverter, the vent being along a downstream surface of the flowdiverter.
 22. The thermal processor of claim 15 wherein the flowdiverter has an upstream end which is bulbous in shape toward the flowof exhaust gases.
 23. A thermal processor for treating a plurality ofsemiconductor articles, comprising:a framework; a furnace heater mountedupon the framework and having a furnace chamber therewithin; aprocessing vessel having a processing chamber for treating thesemiconductor articles, said processing chamber having an outflow with adischarge opening through which heated exhaust gases are discharged; anoutflow cooler connected to receive exhaust gases from the dischargeopening and to remove heat from the exhaust gases; a flow diverterpositioned within the outflow cooler to direct the flow of exhaust gasesagainst walls of the outflow cooler.
 24. The thermal processor of claim23 wherein said flow diverter directs exhaust gases against sidewalls ofthe outflow cooler.
 25. The thermal processor of claim 23 wherein saidflow diverter is an annular flow diverter coaxially positioned withinthe outflow cooler to direct the flow of exhaust gases against sidewallsof the outflow cooler.
 26. The thermal processor of claim 23 whereinsaid outflow cooler further includes:a casing to which the heatexchanger is mounted to remove heat therefrom; a liner mounted withinthe casing in contact therewith to transfer heat through the liner intothe casing.
 27. The thermal processor of claim 23 wherein said outflowcooler further includes:a casing to which the heat exchanger is mountedto remove heat therefrom; a liner mounted within the casing in contacttherewith to transfer heat through the liner into the casing; andwherein the flow diverter is positioned within the outflow cooler todirect the flow of exhaust gases against sidewalls of the outflowcooler.
 28. The thermal processor of claim 23 wherein the flow diverteris an annular member.
 29. The thermal processor of claim 23 wherein theflow diverter has a thin shell.
 30. The thermal processor of claim 23wherein the flow diverter has a thin shell and a vent which allows gasesto move into or from the interior of the flow diverter.
 31. The thermalprocessor of claim 23 wherein the flow diverter has a thin shell and avent which allows gases to move into or from the interior of the flowdiverter, said flow diverter resting on feet to support the diverteraway from walls of the outflow cooler.
 32. The thermal processor ofclaim 23 wherein the flow diverter has a thin shell and a vent whichallows gases to move into or from the interior of the flow diverter, thevent being along a downstream surface of the flow diverter.
 33. Thethermal processor of claim 23 wherein the flow diverter has an upstreamend which is bulbous in shape toward the flow of exhaust gases.
 34. Athermal processor for treating a plurality of semiconductor articles,comprising:a framework; a furnace heater mounted upon the framework andhaving a furnace chamber therewithin; a processing vessel having aprocessing chamber for treating the semiconductor articles, saidprocessing chamber having an outflow with a discharge opening throughwhich heated exhaust gases are discharged; an outflow cooler connectedto receive exhaust gases from the discharge opening and to remove heatfrom the exhaust gases; a casing forming a part of the outflow cooler; aheat exchanger connected to the casing to remove heat therefrom; a linermounted within the casing in contact therewith to transfer heat throughthe liner into the casing, the liner being provided with at least oneshoulder which bears upon the casing to provide support of the liner bythe casing.
 35. A thermal processor according to claim 34 wherein saidat least one shoulder bears upon a shoulder formed in the casing.
 36. Athermal processor according to claim 34 wherein said at least oneshoulder bears upon a shoulder formed in the casing near a bottom end ofthe casing.
 37. A thermal processor according to claim 34 wherein saidat least one shoulder bears upon a shoulder formed in the casing near abottom end of the casing;and further comprising a flow diverterpositioned within the outflow cooler to direct the flow of exhaust gasesagainst walls of the liner, said flow diverter being supported upon saidat least one shoulder of the lining.
 38. The thermal processor of claim37 wherein the flow diverter is an annular member.
 39. The thermalprocessor of claim 37 wherein the flow diverter has a thin shell. 40.The thermal processor of claim 37 wherein the flow diverter has a thinshell and a vent which allows gases to move into or from the interior ofthe flow diverter.
 41. The thermal processor of claim 37 wherein theflow diverter has a thin shell and a vent which allows gases to moveinto or from the interior of the flow diverter, said flow diverterresting on feet to support the diverter away from walls of the outflowcooler.
 42. The thermal processor of claim 37 wherein the flow diverterhas a thin shell and a vent which allows gases to move into or from theinterior of the flow diverter, the vent being along a downstream surfaceof the flow diverter.
 43. The thermal processor of claim 37 wherein theflow diverter has an upstream end which is bulbous in shape toward theflow of exhaust gases.